Raman Spectroscopy of Thin FilmsVincent Lewis ’20, Frank Peiris

Kenyon College Summer Science 2017

AbstractRamanSpectroscopyisapowerfulexperimentaltechniquetoanalyzethevibrationalmodesofthinfilms.UsingRamanSpectroscopy,wehaveinvestigatedzirconiainordertodeciphertheirvibrationalmodesandtoexplorethequalityofsample.Thezirconiawasdepositedonsiliconsubstrates,treatedwitheitherOleicAcidorTrioctylphosphine oxide(TOPO),andthencalcinedatspecifictemperatures.Usingacombinationofresultsfrom632nmand532nmlaserspectroscopy,wefoundthatthezirconiaunderwentcrystalphasetransformationaround700to900degreesCelsius.ThespectraofthezirconiatreatedwithTOPOshowedstrongsignsofbothmonoclinicandtetragonalcrystalstructure,resultswhichwereverifiedbyX-raydiffractionaswell.

WealsousedAtomicForceMicroscopytoexplorethetopographyofthezirconiasamples.Fromtheseimageswewereabletocalculatetherootmeansquare,whichistheaverageroughnessofthesurface.

Raman Spectroscopy

Background

Zirconia Samples

Raman Spectra AFM

Conclusions

References1. https://images.nature.com/full/nature-assets/nprot/journal/v11/n4/images_article/nprot.2016.036-F1.jpg2. https://pharm.virginia.edu/files/2014/01/AFM2.jpg3. A. Muñoz Tabares, José & J. Anglada, Marc. (2010). Quantitative Analysis of Monoclinic Phase in 3Y-TZP by Raman Spectroscopy. Journal of the American Ceramic Society. 93. 1790 -1795

AcknowledgmentsThis work was funded by NIH R15 ES011130 to WHP and by the Kenyon College Summer Science Scholars program.

• TheRamanEffect,otherwiseknownasRamanScattering,istheinelasticscatteringofaphotonduetoexcitedvibrationalmodesofamaterial.

• Byshootingalaseratathinfilm,wecanexcitenewvibrationalmodesofamaterial.Sincetheexcitinglaserisinfluencedbythevibrationalmodes,thephotonscanloseorgainenergy.

• WhiletheRayleighScatteringisbyfarthedominantphenomena,RamanScatteringstilloccurs.Thisshiftonlyoccurswithinonepermillionsofthereflectedphotons,andisthusunobservabletothenakedeye.

• ARamanSpectrometerisabletofilteroutalotofthosereflectedphotons,andgraphaspectrumoftheshifts.Thisisonlypossiblethroughexcitationwithasinglewavelength,asnotchfilterscanbeoptimized.

TOPOZirconia• FromourdatawefoundthatTOPOzirconiabeganto

undergoaphasetransformationaround700C.• At900C,theTOPOzirconiahasbothmonoclinicand

tetragonalstructure.• ThisresultswereconfirmedbyX-raydiffraction.OAZirconia• TheOleicAcidzirconiaonlyshowedatetragonal

crystalstructureathighertemperatures.• Theseresultswerealsoconfirmedbyx-raydiffraction.

Analyzing Spectra

• ZirconiumDioxide(zirconia)isacompoundwithmanyemergingusesinindustry

• ZirconiawasspincoatedonSiliconsubstrates,andthentreatedwitheithertrioctylphosphine oxide(TOPO)oroleicacid(OA).

• Thesechemicalsaffectthecrystalphasesofthezirconia.Zirconiacanforminamorphous,monoclinic,tetragonal,andcubicstructures.Thesephasesarereachedthroughexposuretotemperature.Oursampleswereannealedfor168hoursatdifferenttemperaturesrangingfrom300Cto900C.

300COA

AtomicForceMicroscopy• AtomicForceMicroscopy(AFM)usesa

cantilevertomeasureforceonthesurfaceofamaterial.

• Asthecantileverrunsacrossthetopofthematerial,fluctuationsinthesurfaceheightwillapplydifferentforces.

• Piezoelectronics areabletomovethesampleatfinelytunedincrements,whilealaserisreflectedoffofthecantilever.Thepositionofthethelaserisrecordedbyaphotodiode.

• Bycomparingthedisplacementofthelaserwiththedisplacementofthesamplebythepiezoelectronics,weareabletocreateatopographyofthesample.

TOPO

OleicAcid

Vibrationmodesofmonoclinicandtetragonalzirconia[3]

Astheannealingtemperatureincreases,shownintheAFMimages,theindividualcrystallinesizesdecrease.Athightemperatures,thecrystallinesizescorrespondedtotheexpectedzirconiananoparticlesizes

600COA

700COA

TOPO OleicAcid

300CTOPO

900COA

400CTOPO

600CTOPO 800CTOPO

• PicturedaboveareportionsoftheRamanspectraforbothTOPOandOleicAcid

• PicturedtotheupperrightisagraphofgeneralRamanspectraforzirconia,bothmonoclinic,zirconia,andmixedcrystalstructures

• Colorcodedarespecificpeaksatwavenumberscorrespondingtovibrationalenergylevelsofspecificcrystallinestructures

• At146and260𝑐𝑚#$, tetragonalpeaksexist.

• Ataround180and190𝑐𝑚#$,adoublemonoclinicpeakexists.

• Theremainingpeaksinthespectra(suchastheonearound300)arefromthesiliconsubstrate.

• PicturedinthelowerrightisaspectrumofSiliconobtainedinourlab.Thesepeaksalsoappearintheabovespectrabecauseofthesubstrate.

DiagramofAFM[2]

DiagramofRaman[1]

AFM• Thecrystalsizesinimagesweobtained

correspondedtothenanocrystalsizesofzirconia.

300℃ 400℃ 600℃ 700℃ 800℃ 900℃

RamanSpectrumofSiliconin𝑐𝑚#$